Bootstrapping Perl

This blog post shows a simple, hands-off, automated way to get yourself a Perl environment in user land. If you already know enough about all of this to do it the hard way, and you prefer that, then this post is not aimed at you.

Here's what we are going to achieve:

• Set up a Perl 5.24 installation
• Set up your environment so you can install modules
• Set up your project so you can install its dependencies

These are the things people seem to struggle with a lot, and the instructions are piecemeal all over the internet. Here they are all standing in a row.

Perlbrew your Perl 5.24

As this blog post becomes older, that number will get bigger, so make sure to alter it if you copy this from the future.

Do this as root:

Debian

apt-get install perlbrew

FreeBSD

fetch -o- https://install.perlbrew.pl | sh

Whatever else

curl -L https://install.perlbrew.pl | bash

Windows

Haha, yeah, right.

Once you've installed perlbrew, log out of root and init it as your user. Then install a perl. This will take a while.

perlbrew init
perlbrew install perl-5.24.0

There, you now have a Perl 5.24.0 installation in your home folder. which perl will still say /usr/bin/perl so you can change that:

perlbrew switch perl-5.24.0

It will have already told you that you need to alter your .bashrc or suchlike, with something like this:

source $HOME/perl5/perlbrew/etc/bashrc

You should do that.

Perlbrew does other stuff - see https://perlbrew.pl for details.

cpanm

You want to be able to install modules against your new perl.

You will have to reinstall modules under every perl you have if you want to use the same modules under different versions. This is because of reasons.¹

perlbrew install-cpanm

Now you can use cpanm to install modules. If you install a new Perl with perlbrew, you will have to

perlbrew switch $your_new_perl
perlbrew install-cpanm

All over again. If you're dealing with multiple Perl versions for a reason, you've probably already read the docs enough that you know which commands to use.

cpanfile

A cpanfile is a file in your project that lists the dependencies it requires. The purpose of this file is for when you are developing a project, and thus you haven't actually installed it. It looks like this.

requires "Moose";
requires "DBIx::Class" => "0.082840";
requires "perl" => "5.24";

test_requires "Test::More";

You use it like this

cpanm --installdeps .

The . refers to the current directory, of course, so you run this from a place that has a cpanfile in it.

The full syntax is on CPAN.

Purpose of cpanfile

A "project" here refers to basically anything you might put on CPAN - a distribution. It might be a module, or just some scripts, or a whole suite of both of those things.

The point is it's a unit, and it has dependencies, and you can't run the code without satisfying those dependencies.

If you install this distribution with cpanm then it will automatically install the dependencies because the author set up the makefile correctly so that cpanm knew what the dependencies were. cpanm also puts the modules in $PERL5LIB and the scripts in $PATH so that you can use them.

If you have the source code, either you are the author, or at least you're a contributor; you don't want to run the makefile just to install the dependencies, because this will install the development version of the module too. Nor do you want to require your contributors to install the whole of dzil just to contribute to your module. So, you provide a cpanfile that lists the dependencies they require to run or develop your module or scripts.

^{1 The primary reason is that every Perl version has a slightly different set of development headers, so any modules written in C will be incompatible. It's too much effort to separate them and disk space is cheap; so we just keep separate libraries and avoid the problem.}